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billonwheels 12-11-2012 08:10 PM

what size alternator
 
My buddy has a 1972 pontiac Lemans with a 400 bored 30 over. His generator light comes on while driving. Is the alternator going bad? its still a 3 wire i think. What ampreage will he need?

bob70 12-11-2012 08:31 PM

I am by no means an expert but I do know that the alternator size requirement is a function of the amperage draw of the various electrical accessories on the car. That's the place to start. What's the max potential amp draw assuming likely accessories to be on at the same time?

Before looking for a higher amp alternator, I think I'd make sure the current one is doing what it's supposed to do. If your friend hasn't a clue about this stuff, then he'd probably be wise to seek some professional advice/troubleshooting.

66GMC 12-11-2012 08:43 PM

According to my NAPA Prolink electronic catalog, there were 4 possible alternators on that year/make/model:

https://partimages.genpt.com/partimages/159702.jpg
2 that were 55-63 Amp "small frame - 10SI" ... (1 with single groove, 1 with double groove pulley)
================================================== ==
https://partimages.genpt.com/partimages//657224.jpg
There were also 2, 80 Amp "large-frame - 27SI" alternators ... again offered in single and double groove pulley versions. These alternators had a 2-leg lower mount and were an "HD option" on these cars. They were usually on the well-equipped models with AC, power seats, rear defrost, etc.

Most Delco alternators have a Delco-Remy ID number stamped into the front half of the case along with the Amp rating. It is also common practice for rebuilders to grind these numbers off of a "rebuildable core" and affix their own identification label or tag according to the rebuild specs.

IF it is still there, it will be all numeric ... something like "1101015" followed by "80A"

I can help to idenify it further if that stamping info is still available, or you can browse the
Wilson e-CAT

Note that the Wilson catalog only list 1 of each series, because their alternators are not supplied with new pullies.

billonwheels 12-11-2012 09:17 PM

thanks guys, He's not running any high current audio system, just the factory stuff. He was asking me about remans and I was telling hime he couldnt wrong with an upgrade.

66GMC 12-11-2012 09:30 PM

Quote:

Originally Posted by billonwheels (Post 1621781)
thanks guys, He's not running any high current audio system, just the factory stuff. He was asking me about remans and I was telling hime he couldnt wrong with an upgrade.

Yes, "upgrading" from a 63 Amp to an 80 Amp wouldn't hurt anything, but he would have to have the correct mounts. Look at the two pics in my previous post ... they mount up differently.

IF he has a 63 Amp (small-frame) alternator, a shop that specializes in electrical rebuilding could overhaul it and install a "Y-wound" stator for that 80+ Amp output.


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